# CVE-2026-53501: Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature

> Attackers can bypass HMAC validation in Thumbor by manipulating URL signatures, allowing unauthorized access to images from unintended domains or paths.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jul 2026
- **Updated:** 31 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-53501, GHSA-mw3h-qjxj-6xg9, PYSEC-2026-3620, UBUNTU-CVE-2026-53501

## What is CVE-2026-53501?

CVE-2026-53501 is a high-severity vulnerability in thumbor, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor’s HMAC validation can be bypassed due to the use of Python’s .replace() when removing the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation. This allows crafting URLs where the validated string differs from the actual requested resource, enabling loading images from unintended domains or paths. This issue is fixed in 7.8.0.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-53501?

3 open source packages ship an affected version, including thumbor.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `thumbor` | PyPI | All versions | 7.8.0 |
| `thumbor` | PyPI | All versions | 7.8.0 |
| `thumbor` | PyPI | All versions | 7.8.0 |

## How do I fix CVE-2026-53501?

Upgrade thumbor to 7.8.0 or later.

## Is CVE-2026-53501 being exploited?

There is no known exploitation of CVE-2026-53501 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53501 and fix it if it is affected.

What it is: CVE-2026-53501 is a high-severity vulnerability in thumbor, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53501 in the wild and no public exploit code.

Affected packages and fixed versions:
- thumbor (PyPI): affected all versions; fixed in 7.8.0
- thumbor (PyPI): affected all versions; fixed in 7.8.0
- thumbor (PyPI): affected all versions; fixed in 7.8.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-53501/ (Markdown: https://insights.sbomify.com/CVE-2026-53501/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53501
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53501
- OSV: https://osv.dev/vulnerability/CVE-2026-53501

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53501/
Summaries are generated and may contain mistakes; the official description above is the record.